For UV-curing materials it is known that some hydroxyarylketones and diaryl ketones are useful photo-initiators for the photopolymerizations of ethylenically unsaturated systems. As structured below, examples of hydroxyarylketone-type photo-initiators are so-called Darocur 1173 (2-hydroxy-2-methyl-1-phenylpropan-1-one) and Irgacure 184 ((1-hydroxycyclohexyl)(phenyl)methanone), and examples of diarylketone-type photo-initiators are benzophenone (BP) and [1,1′-biphenyl]-4-yl(phenyl)methanone (PBZ). These compounds are all commercially available and serve as some of the most important benchmark photo-initiators widely used today.

However, while functioning the relevant photochemical cleavage reactions of these compounds generally lead to emissions of various substances such as benzene, benzaldehyde, acetone, cyclohexanone etc, which are usually highly volatile, harmful, and even carcinogenic, and are thus sometimes classified as undesirable VOCs (abbreviation for Volatile Organic Compounds). Not surprisingly, environmental pollution as well as health threat issues arising from such harmful emissions have been experiencing increasing levels of public attention and legislative regulations. Consequently, several patent disclosures have been devoted to exploring potential solutions to these significant challeneges through designs and preparations of new compounds, for examples, Chinese patent applications CN1288123C, CN1529588A, CN1914560A, CN100548955C, CN100523007C, CN1832912A, CN1942424A, and United States patent applications US2006/0270748A1, 2010/0104979A1, US2005/0239971A1, and U.S. Pat. No. 4,739,052. As shown below, some representative chemical structures of such “new-generation” photo-initiator compounds are Irgacure 127 [1,1′-(methylenebis(4,1-phenylene))bis(2-hydroxy-2-methylpropan-1-one)] and bifunctional hydroxyketones A-C. It should be emphasized that, without any exception, in these reported structures the photo-active hydroxyketone functionality and the ring substituent always display para-aromatic ring substitution pattern. This is not surprising since the stepwise installation of hydroxyketone functionality to an aromatic ring must follow the principle of so-called Friedel-Crafts acylation reaction, that is, acylation on an aromatic ring bearing an electron-releasing substituent (such as an alkyl group) would occur at the site that is para- to that substituent.

These known disclosures collectively reflect a strong market demand for developing new generations of environment as well as health-friendly photo-initiator products, particularly those that can help tackle the aforementioned drawbacks associated with the uses of conventional photo-initiators, including reduction or elimination of emissions of harmful VOCs, carcinogenic aromatic hydrocarbons, and unpleasant residual odors. Moreover, equally important measure of the potential usefulness of these new products is their practicality, i.e., they will have to address the above-mentioned challenges while at the same time maintain cost-effectiveness.